Mixture of visible light-responsive photocatalytic titanium oxide fine particles, dispersion liquid thereof, method for producing dispersion liquid, photocatalyst thin film, and member having photocatalyst thin film on surface

ABSTRACT

Provided are the following: a mixture of visible light-responsive photocatalytic titanium oxide fine particles which can conveniently produce a photocatalyst thin film that exhibits photocatalyst activity even with only visible light (400-800 nm) and that exhibits high transparency; a dispersion liquid of the fine particles; a method for producing the dispersion liquid; a photocatalyst thin film; and a member having the photocatalyst thin film on a surface thereof. The mixture of visible light-responsive photocatalytic titanium oxide fine particles is characterized by containing two kinds of titanium dioxide fine particles: first titanium oxide fine particles, in which a tin component and a transition metal component (excluding an iron group element component) that increases visible light response properties form a solid solution, and second titanium oxide fine particles, in which an iron group element component and a chromium group element component form a solid solution.

TECHNICAL FIELD

The present invention relates to a visible light-responsivephotocatalytic titanium oxide fine particle mixture, a dispersionthereof, a method for preparing the dispersion, a photocatalytic thinfilm formed using the dispersion, and a member having the photocatalyticthin film formed thereon. More particularly, the invention relates to avisible light-responsive photocatalytic titanium oxide fine particlemixture which can easily produce a photocatalytic thin film that has ahigh transparency and manifests a photocatalytic activity even undervisible light (400 to 800 nm) alone, a dispersion thereof, a method forpreparing the dispersion, a photocatalytic thin film, and a memberhaving the photocatalytic thin film on the surface.

BACKGROUND ART

Photocatalytic titanium oxide fine particles are frequently used in suchapplications as the cleaning, deodorization and disinfection ofsubstrate surfaces. As used herein, “photocatalytic reaction” refers toa reaction caused by excited electrons and holes generated due to theabsorption of light by titanium oxide. The decomposition of organicmatter is thought to arise primarily by the following mechanisms: (1)the excited electrons and holes that have formed carry outoxidation-reduction reactions with oxygen and water adsorbed on thetitanium oxide surface, generating active species, which decomposeorganic matter; and (2) the holes that have formed directly oxidize anddecompose organic matter adsorbed on the titanium oxide surface.

Studies have been carried out recently which attempt to apply suchphotocatalysis not only to outdoor uses where ultraviolet light can beutilized, but also to indoor spaces illuminated with light sources suchas fluorescent lamps that emit primarily visible-spectrum light(wavelength, 400 to 800 nm). For example, a tungsten oxidephotocatalytic body has been disclosed as a visible light-responsivephotocatalyst (JP-A 2009-148700; Patent Document 1), but becausetungsten is a scarce element, there exists a desire for improvements inthe visible light activity of photocatalysts that utilize the widelyavailable element titanium.

Methods for increasing the visible light activity of photocatalystswhich use titanium oxide include methods that entail supporting iron orcopper on the surface of titanium oxide fine particles or metal-dopedtitanium oxide fine particles (see, for example, JP-A 2012-210632:Patent Document 2; JP-A 2010-104913: Patent Document 3; JP-A2011-240247: Patent Document 4; and JP-A H07-303835: Patent Document 5);and a method which separately prepares titanium oxide fine particlescontaining in solid solution (i.e., doped with) tin and a transitionmetal that increases the visible light activity and titanium oxide fineparticles containing copper in solid solution, and then uses theseseparately prepared particles in admixture (WO 2014/045861: PatentDocument 6).

The latter of these methods (Patent Document 6), that is, the methodwhich separately prepares titanium oxide fine particles containing insolid solution tin and a transition metal that increases the visiblelight activity and titanium oxide fine particles containing copper insolid solution and then uses these separately prepared particles inadmixture, has the advantage that because the metals other than titaniumthat are used are all contained in solid solution in the titanium oxidefine particles, the particles are stable and do not readily deteriorate,enabling a photocatalytic thin film of high durability to be obtained.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A 2009-148700

Patent Document 2: JP-A 2012-210632

Patent Document 3: JP-A 2010-104913

Patent Document 4: JP-A 2011-240247

Patent Document 5: JP-A H07-303835

Patent Document 6: WO 2014/045861

SUMMARY OF INVENTION Technical Problem

In light of the above circumstances, one object of this invention is toprovide, by combining and mixing together titanium oxide fine particlescontaining different transition metals in solid solution, a visiblelight-responsive photocatalytic titanium fine particle mixture capableof achieving a high visible light activity of a type differing from thatin the prior art. Further objects are to provide a dispersion thereof, amethod for preparing the dispersion, a photocatalytic thin film formedusing the dispersion, and a member having the photocatalytic thin filmon the surface thereof.

Solution to Problem

One approach taken by the inventors to achieve the above objects hasbeen to conduct a search for new materials which exhibit a highphotocatalytic activity under visible light-only condition by varyingthe second type of titanium oxide fine particle that is combined with,as the first type of titanium oxide fine particle used in PatentDocument 4 being titanium oxide fine particle containing in solidsolution both tin and a transition metal that increases the visiblelight activity. The titanium oxide fine particle containing a copperconstituent in solid solution which serves as the second type oftitanium oxide fine particle used in Patent Document 4 exhibits somephotocatalytic activity even under visible light (400 to 800 nm) onlycondition. However, in the course of this investigation, the inventorshave made the unexpected discovery that when titanium oxide fineparticle containing an iron-group element constituent in solid solution,which hardly exhibits photocatalytic activity under visible light-onlycondition, is included as the second type of titanium oxide fineparticle, under visible light-only condition, a photocatalytic activityis exhibited which is as high as that obtained with the use of titaniumoxide fine particle containing a copper constituent in solid solution.

The inventors have conducted further detailed investigations on cases inwhich titanium oxide fine particle containing this iron-group elementconstituent in solid solution is included as the second type of titaniumoxide fine particle, whereupon they have learned that when acetaldehydegas present within air is decomposed under visible light, a todecomposition activity can be obtained even in a low-concentrationregion where such activity has been difficult to achieve with prior-artmaterials, and that it is possible, within a significant length of timeunder visible light condition, to lower the level to 0.03 ppm or below,which is the indoor concentration guideline value for a chemicalsubstance (acetaldehyde) within indoor air established by the JapaneseMinistry of Health, Labor and Welfare. They have also found that thedecomposition activity rises when a chromium-group element constituentis additionally included in solid solution in the titanium oxide fineparticle containing an iron-group element constituent in solid solution.That is, the inventors have discovered that, by using a photocatalyticfilm formed using a visible light-responsive photocatalytic titaniumoxide fine-particle dispersion containing both a first type of titaniumoxide fine particle that contains in solid solution tin and a transitionmetal which increases visible light activity and a second type oftitanium oxide fine particle that contains in solid solution aniron-group element constituent and a chromium-group element constituent,even in cases where the substrate to be decomposed is at a lowconcentration that has heretofore been difficult to decompose undervisible light condition, a high decomposition activity can be obtained.

Accordingly, this invention provides the following visiblelight-responsive photocatalytic titanium oxide fine particle mixture,dispersion thereof, method for preparing the dispersion, and memberhaving on the surface thereof the photocatalytic thin film formed usingthe dispersion.

[1]

A visible light-responsive photocatalytic titanium oxide fine particlemixture containing two types of titanium oxide fine particles: a firsttype of titanium oxide fine particle containing in solid solution a tinconstituent and a transition metal constituent (exclusive of aniron-group element constituent) that increases visible lightresponsiveness, and a second type of titanium oxide fine particlecontaining in solid solution an iron-group element constituent and achromium-group element constituent.

[2]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of [1], wherein the first type of titanium oxide fine particleand the second type of titanium oxide fine particle have a mixing ratiotherebetween, expressed as the weight ratio [(first type of titaniumoxide fine particle)/(second type of titanium oxide fine particle)], offrom 99 to 0.01.

[3]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of [1] or [2], wherein the amount of the tin constituentincluded in the first type of titanium oxide fine particle, expressed asa molar ratio with titanium (Ti/Sn), is from 1 to 1,000.

[4]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of any of [1] to [3], wherein the transition metal constituentcontained in solid solution in the first type of titanium oxide fineparticle is at least one selected from the group consisting of vanadium,chromium, manganese, niobium, molybdenum, rhodium, antimony, tungstenand cerium.

[5]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of [4], wherein the transition metal constituent contained insolid solution in the first type of titanium oxide fine particle is atleast one selected from the group consisting of molybdenum, tungsten andvanadium.

[6]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of [5], wherein the amount of the molybdenum or tungstenconstituent included in the first type of titanium oxide fine particle,expressed as a molar ratio with titanium (Ti/Mo or Ti/W), is from 1 to1,000.

[7]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of [5], wherein the amount of the vanadium constituent includedin the first type of titanium oxide fine particle, expressed as a molarratio with titanium (Ti/V), is from 10 to 10,000.

[8]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of any of [1] to [7], wherein the amount of the iron-groupelement constituent included in the second type of titanium oxide fineparticle, expressed as a molar ratio with titanium (Ti/iron groupelement), is from 1 to 1,000.

[9]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of any of [1] to [8], wherein the iron-group element constituentcontained in solid solution in the second type of titanium oxide fineparticle is an iron constituent.

[10]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of any of [1] to [9], wherein the amount of the chromium-groupelement constituent included in the second type of titanium oxide fineparticle, expressed as a molar ratio with titanium (Ti/chromium-groupelement), is from 1 to 1,000.

[11]

The visible light-responsive photocatalytic titanium oxide fine particlemixture of any of [1] to [10], wherein the chromium-group elementconstituent contained in solid solution in the second type of titaniumoxide fine particle is at least one selected from the group consistingof a molybdenum constituent and a tungsten constituent.

[12]

A visible light-responsive photocatalytic titanium oxide fine particledispersion comprising two types of titanium oxide fine particlesdispersed in an aqueous dispersion medium: a first type of titaniumoxide fine particle containing in solid solution a tin constituent and atransition metal constituent (exclusive of an iron-group elementconstituent) that increases visible light responsiveness, and a secondtype of titanium oxide fine particle containing in solid solution aniron-group element constituent and a chromium-group element constituent.

[13]

The visible light-responsive photocatalytic titanium oxide fine particledispersion of [12], further including a binder.

[14]

The visible light-responsive photocatalytic titanium oxide fine particledispersion of [13], wherein the binder is a silicon compound-basedbinder.

[15]

A photocatalytic thin film comprising the visible light-responsivephotocatalytic titanium oxide fine particle mixture of any of [1] to[11].

[16]

The photocatalytic thin film of [15], further including a binder.

[17]

A member in which the photocatalytic thin film of [15] or [16] is formedon the substrate surface.

[18]

A method for preparing a visible light-responsive photocatalytictitanium oxide fine particle dispersion, comprising the steps of:

(1) preparing a tin and transition metal constituent-containingperoxotitanic acid solution from a starting titanium compound, a tincompound, a transition metal compound (exclusive of an iron-groupelement compound), a basic substance, a hydrogen peroxide and an aqueousdispersion medium;

(2) preparing a tin and transition metal constituent-containing titaniumoxide fine particle dispersion by heating at between 80° C. and 250° C.and under pressure control the tin and transition metalconstituent-containing peroxotitanic acid solution obtained in Step (1);

(3) preparing an iron-group element and chromium-group elementconstituent-containing peroxotitanic acid solution from a startingtitanium compound, an iron-group element compound, a chromium-groupelement compound, a basic substance, hydrogen peroxide and an aqueousdispersion medium;

(4) preparing an iron-group element and chromium-group elementconstituent-containing titanium oxide fine particle dispersion byheating at between 80° C. and 250° C. and under pressure control theiron-group element and chromium-group element constituent-containingperoxotitanic acid solution obtained in Step (3); and

(5) mixing together the two types of titanium oxide fine particledispersions prepared in Steps (2) and (4).

Advantageous Effects of Invention

This invention makes it possible to provide a visible light-responsivephotocatalytic titanium oxide fine particle mixture which can easilyproduce a photocatalytic thin film that has a high transparency andmanifests a photocatalytic activity even under visible light (400 to 800nm) alone, a dispersion thereof, a method for preparing the dispersion,and a member having on the surface thereof the photocatalytic thin filmformed using the dispersion.

DESCRIPTION OF EMBODIMENTS

The inventive visible light-responsive photocatalytic titanium oxidefine particle mixture, dispersion thereof, method for preparing thedispersion, and member having on the surface thereof the photocatalyticthin film are described more fully below.

The visible light-responsive photocatalytic titanium oxide fine particlemixture of the invention is a mixture that includes titanium oxide fineparticles of mutually differing compositions which are referred toherein as a first type of titanium oxide fine particle and a second typeof titanium oxide fine particle. It is desirable in particular to usethis mixture as a dispersion.

<Visible Light-Responsive Photocatalytic Titanium Oxide Fine ParticleDispersion>

The visible light-responsive photocatalytic titanium oxide fine particledispersion of the invention is made up of titanium oxide fine particlesof mutually differing compositions, namely a “first type” of titaniumoxide fine particle and a “second type” of titanium oxide fine particle,those are dispersed in an aqueous dispersion medium. Titanium oxide fineparticle of the first type is titanium oxide fine particle containing insolid solution a tin constituent and a transition metal constituent(exclusive of an iron-group element constituent). Titanium oxide fineparticle of the second type is titanium oxide fine particle containingin solid solution an iron-group element constituent and a chromium-groupelement constituent.

As used herein, “solid solution” refers to a phase in which an atom at alattice point of one crystal phase is substituted with another atom orin which another atom is entered into the lattice interstice, that is,it refers to a mixed phase in which another substance is regarded asdissolved in a certain crystal phase, and is a homogeneous phase as thecrystal phase. A solid solution in which a solvent atom at lattice pointis substituted with a solute atom is called a “substituted solidsolution”, and a solid solution in which a solute atom is entered intothe lattice interstice is called an “interstitial solid solution”. Here,“solid solution” may refer to either of these.

The titanium oxide fine particles of the invention are characterized inthat the first type of titanium oxide fine particle forms a solidsolution with at least some of the tin and transition metal atoms(exclusive of an iron-group element constituent) and the second type oftitanium oxide fine particle forms a solid solution with at least someof the iron-group element constituent and the chromium-group elementconstituent. The solid solution may be either a substituted solidsolution or an interstitial solid solution. A substituted solid solutionis one that is formed by the substitution of titanium sites in thetitanium oxide crystals with various metal atoms, and an interstitialsolid solution is one that is formed with the introduction of variousmetal atoms into lattice interstices in the titanium oxide crystals.When various metal atoms enter into solid solution in titanium oxide,only peaks of the crystal phases of titanium oxide are observed inmeasurement of the crystal phase by x-ray diffraction analysis or thelike, and the peaks of compounds derived from the various metal atomsadded are not observed.

Methods of forming solid solutions of different metals in metal oxidecrystals include, without particular limitation, vapor phase methods(e.g., chemical vapor deposition method, physical vapor depositionmethod), liquid phase methods (e.g., hydrothermal method, sol-gelmethod), and solid phase methods (e.g., high-temperature firing method).

Titanium oxide fine particles are generally known to have three crystalphases: rutile, anatase and brookite. It is preferable to use chieflyrutile and anatase in the first and second type of titanium oxide fineparticle. In particular, it is preferable for the first type of titaniumoxide fine particle to be chiefly rutile and it is preferable for thesecond type of titanium oxide fine particle to be chiefly anatase.“Chiefly” here means generally at least 50 wt %, preferably at least 70wt %, and more preferably at least 90 wt %, and may even be 100 wt %, ofall the titanium oxide fine-particle crystals.

The dispersion medium used in the dispersion is typically an aqueoussolvent, with the use of water being preferred, although a mixed solventof water and a hydrophilic organic solvent that mixes with water in anyratio may be used. The water is preferably, for example, deionizedwater, distilled water or purified water. The hydrophilic organicsolvent is preferably, for example, an alcohol such as methanol, ethanolor isopropanol; a glycol such as ethylene glycol; or a glycol ether suchas ethylene glycol monomethyl ether, ethylene glycol monoethyl ether orpropylene glycol-n-propyl ether. When a mixed solvent is used, the ratioof hydrophilic organic solvent in the mixed solvent is preferably morethan 0 wt % and not more than 50 wt %, more preferably not more than 20wt %, and even more preferably not more than 10 wt %.

The first type of titanium oxide fine particle is a titanium oxide fineparticle which contains in solid solution a tin constituent and atransition metal constituent other than iron group constituent thatincreases the visible light activity. Transition metals are elementsselected from among Groups 3 to 11 of the Periodic Table. The transitionmetal constituent that increases the visible light responsiveness ispreferably selected from among vanadium, chromium, manganese, niobium,molybdenum, rhodium, antimony, tungsten and cerium. Of these, theselection of molybdenum, tungsten or vanadium is preferred.

The tin constituent that forms a solid solution in the first type oftitanium oxide fine particle is used to increase the visible lightresponsiveness of photocatalytic thin films, and may be any tinconstituent derived from a tin compound, such as tin metal (Sn), oxides(SnO, SnO₂), hydroxides, chlorides (SnCl₂, SnCl₄), nitrates (Sn(NO₃)₂),sulfates (SnSO₄), halides and complex compounds. These may be usedsingly or two or more may be used in combination. Of these, the use ofoxides (SnO, SnO₂), chlorides (SnCl₂, SnCl₄) or sulfates (SnSO₄) ispreferred.

The amount of tin constituent included in the first type of titaniumoxide fine particle, expressed as a molar ratio with titanium (Ti/Sn),is from 1 to 1,000, preferably from 2 to 500, and more preferably from 5to 100. When the molar ratio is less than 1, the titanium oxide contentdecreases and a sufficient photocatalytic effect may not be exhibited.When the molar ratio is greater than 1,000, the visible lightresponsiveness may be inadequate.

The transition metal constituent contained in solid solution in thefirst type of titanium oxide fine particle may be any derived from acompound of the transition metal, such as the metal, oxides, hydroxides,chlorides, nitrates, sulfates, halides and various complex compounds.These may be used singly or two or more may be used together.

The amount of the transition metal constituent included in the firsttype of titanium oxide fine particle may be suitably selected accordingto the type of transition metal constituent. However, the amount,expressed as the molar ratio with titanium (Ti/transition metal), ispreferably in the range of 1 to 10,000, and especially the range of 5 to1,000.

Here, when molybdenum is selected as the transition metal constituent tobe included in solid solution in the first type of titanium oxide fineparticle, the molybdenum constituent may be any that is derived frommolybdenum compounds, and is exemplified by molybdenum metal (Mo),oxides (MoO₂, MoO₃), molybdic acid and salts thereof (H₂MoO₄, Na₂MoO₄),hydroxides, chlorides (MoCl₃, MoCl₅), nitrates, sulfates, halides andcomplex compounds. These may be used singly or two or more may be usedin combination. Of these, the use of oxides (MoO₂, MoO₃) or chlorides(MoCl₃, MoCl₅) is preferred.

The amount of the molybdenum constituent included in the first type oftitanium oxide fine particle, expressed as the molar ratio with titanium(Ti/Mo), is from 1 to 1,000, preferably from 2 to 100, and morepreferably from 2 to 50. The reason for this range is that at a molarratio below 1, the titanium oxide content becomes low and a sufficientphotocatalytic effect may not be exhibited, and at a molar ratio greaterthan 1,000, the visible light responsiveness may be inadequate and ahigh decomposition activity at low acetaldehyde concentrations may notbe obtained.

When tungsten is selected as the transition metal constituent to beincluded in solid solution in the first type of titanium oxide fineparticle, the tungsten constituent may be any that is derived fromtungsten compounds, and is exemplified by tungsten metal (W), oxides(WO₃), tungstic acid and salts thereof (H₂WO₄, Na₂WO₄, K₂WO₄),hydroxides, chlorides (WCl₄, WCl₆), nitrates, sulfates, halides andcomplex compounds. These may be used singly or two or more may be usedin combination. Of these, the use of oxides (WO₃), tungstic acid andsalts thereof (H₂WO₄, Na₂WO₄, K₂WO₄), and chlorides (WCl₄, WCl₆) ispreferred.

The amount of the tungsten constituent included in the first type oftitanium oxide fine particle, expressed as the molar ratio with titanium(Ti/W), is from 1 to 1,000, is preferably from 2 to 100, and morepreferably from 2 to 50. The reason for this range is that at a molarratio below 1, the titanium oxide content becomes low and a sufficientphotocatalytic effect may not be exhibited, and at a molar ratio greaterthan 1,000, the visible light responsiveness may be inadequate and ahigh decomposition activity at low acetaldehyde concentrations may notbe obtained.

When vanadium is selected as the transition metal constituent to beincluded in solid solution in the first type of titanium oxide fineparticle, the vanadium constituent may be any that is derived fromvanadium compounds, and is exemplified by vanadium metal (V), oxides(VO, V₂O₃, VO₂, V₂O₅), hydroxides, chlorides (VCl₅), oxychloride(VOCl₃), nitrates, sulfates, oxysulfate (VOSO₄), halides and complexcompounds. These may be used singly or two or more may be used incombination. Of these, the use of oxides (V₂O₃, V₂O₅), chlorides (VCl₅),oxychloride (VOCl₃) or oxysulfate (VOSO₄) is preferred.

The amount of the vanadium constituent included in the first type oftitanium oxide fine particle, expressed as the molar ratio with titanium(Ti/V), is from 10 to 10,000, preferably from 100 to 10,000, and morepreferably from 100 to 5,000. The reason for this range is that at amolar ratio below 10, the titanium oxide crystal content becomes low anda sufficient photocatalytic effect may not be exhibited, and at a molarratio greater than 10,000, the visible light responsiveness may beinadequate and a high decomposition activity at low acetaldehydeconcentrations may not be obtained.

A plurality of elements from among molybdenum, tungsten and vanadium maybe selected as the transition metal constituent contained in solidsolution in the first type of titanium oxide fine particle. Theirrespective amounts in this case may be selected from the above ranges,provided that the molar ratio between the sum of these amounts and theamount of titanium, expressed as [Ti/(Mo+W+V)], is at least 1 and lessthan 10,000.

The first type of titanium oxide fine particle may be of one kind usedalone, or may be of two or more kinds used in combination. When two ormore kinds having differing visible light responsivenesses are combined,a visible light activity-increasing effect may be obtained.

The second type of titanium oxide fine particle has a composition thatdiffers from that of the first type of titanium oxide fine particle andis characterized by containing in solid solution an iron-group elementconstituent and a chromium-group element constituent. The general formis one which, unlike the first type of titanium oxide fine particle,includes no transition metal other than an iron-group elementconstituent and a chromium-group element constituent, and includes alsono tin.

The iron group metal contained in solid solution in the second type oftitanium oxide fine particle is exemplified by iron, cobalt and nickel.Of these, iron is preferred.

The chromium group metal contained in solid solution in the second typeof titanium oxide fine particle is exemplified by chromium, molybdenumand tungsten. Of these, molybdenum and tungsten are preferred.

The iron-group element constituent contained in solid solution in thesecond type of titanium oxide fine particle may be any that is derivedfrom iron-group element compounds, such as iron metal (Fe), oxides(Fe₂O₃, Fe₃O₄), hydroxides (FeO(OH)), chlorides (FeCl₂, FeCl₃), nitrates(Fe(NO₃)₃), sulfates (FeSO₄, Fe₂(SO₄)₃), halides and complex compounds.These may be used singly or two or more may be used in combination. Ofthese, the use of oxides (Fe₂O₃, Fe₃O₄), hydroxides (FeO(OH)), chlorides(FeCl₂, FeCl₃), nitrates (Fe(NO)₃) and sulfates (FeSO₄, Fe₂(SO₄)₃) ispreferred.

The amount of the iron-group element constituent included in the secondtype of titanium oxide fine particle, expressed as the molar ratio withtitanium (Ti/iron group element), is from 1 to 1,000, preferably from 2to 200, and more preferably from 5 to 100. The reason for this range isthat at a molar ratio below 1, the titanium oxide content becomes lowand a sufficient photocatalytic effect may not be exhibited, and at amolar ratio greater than 1,000, the visible light responsiveness may beinadequate.

When molybdenum is selected as the chromium-group element constituent tobe included in solid solution in the second type of titanium oxide fineparticle, the molybdenum constituent may be any that is derived frommolybdenum compounds, and is exemplified by molybdenum metal (Mo),oxides (MoO₂, MoO₃), molybdic acid and salts thereof (H₂MoO₄, Na₂MoO₄),hydroxides, chlorides (MoCl₃, MoCl₅), nitrates, sulfates, halides andcomplex compounds. These may be used singly or two or more may be usedin combination. Of these, the use of oxides (MoO₂, MoO₃) and chlorides(MoCl₃, MoCl₅) is preferred.

The amount of the molybdenum constituent included in the second type oftitanium oxide fine particle, expressed as the molar ratio with titanium(Ti/Mo), is from 1 to 1,000, preferably from 2 to 100, and morepreferably from 2 to 50. The reason for this range is that at a molarratio below 1, the titanium oxide content becomes low and a sufficientphotocatalytic effect may not be exhibited, and at a molar ratio greaterthan 1,000, the visible light responsiveness may be inadequate and ahigh decomposition activity at low acetaldehyde concentrations may notbe obtained.

When tungsten is selected as the chromium-group element constituent tobe included in solid solution in the second type of titanium oxide fineparticle, the tungsten constituent may be any that is derived fromtungsten compounds, and is exemplified by tungsten metal (W), oxides(WO₃), tungstic acid and salts thereof (H₂WO₄, Na₂WO₄, K₂WO₄),hydroxides, chlorides (WCl₄, WCl₆), nitrates, sulfates, halides andcomplex compounds. These may be used singly or two or more may be usedin combination. Of these, the use of oxides (WO₃), tungstic acid andsalts thereof (H₂WO₄, Na₂WO₄, K₂WO₄), and chlorides (WCl₄, WCl₆) ispreferred. When molybdenum or tungsten is used as the transition metalin the first type of titanium oxide fine particle, it is even moredesirable to use molybdenum or tungsten as the chromium-group element inthe second type of titanium oxide fine particle as well.

The amount of the tungsten constituent included in the second type oftitanium oxide fine particle, expressed as the molar ratio with titanium(Ti/W), is from 1 to 1,000, preferably from 2 to 100, and morepreferably from 2 to 50. The reason for this range is that at a molarratio below 1, the titanium oxide content becomes low and a sufficientphotocatalytic effect may not be exhibited, and at a molar ratio greaterthan 1,000, the visible light responsiveness may be inadequate and ahigh decomposition activity at low acetaldehyde concentrations may notbe obtained.

It is preferable to select molybdenum and/or tungsten as thechromium-group element constituent that is contained in solid solutionin the second type of titanium oxide fine particle, the molar ratiobetween the titanium and the sum of the respective amounts of thechromium, molybdenum and tungsten constituents, expressed as [Ti/(totalamount of chromium-group elements)], being at least 1 and up to 1,000.The second type of titanium oxide fine particle may be of one kind usedalone, or may be of two or more kinds used in combination. When two ormore kinds having differing visible light responsivenesses are combined,a visible light activity-increasing effect may be obtained.

The first type of titanium oxide fine particle and second type oftitanium oxide fine particle in the visible light-responsivephotocatalytic titanium oxide fine particle mixture have a volume-based50% cumulative distribution size (D₅₀) measured by dynamic laser lightscattering (which size is also referred to below as the “averageparticle size”) of preferably from 5 to 30 nm, and more preferably from5 to 20 nm. This is because, at an average particle size below 5 nm, thephotocatalytic activity may be inadequate, and at more than 30 nm, thedispersion may become opaque. Instruments that may be used to measurethe average particle size include, for example, the Nanotrac UPA-EX150(Nikkiso Co., Ltd.) and the LA-910 (Horiba, Ltd.).

The first type of titanium oxide fine particle and the second type oftitanium oxide fine particle included in the visible light-responsivephotocatalytic titanium oxide fine particle mixture have a mixing ratiotherebetween, expressed as the weight ratio [(first type of titaniumoxide fine particle)/(second type of titanium oxide fine particle)], ofpreferably from 99 to 0.01, more preferably from 19 to 0.05, and evenmore preferably from 10 to 0.5. This is because, at a weight ratio inexcess of 99 or below 0.01, the visible light activity may beinadequate.

From the standpoint of the ease of forming a photocatalytic thin film ofthe required thickness, the total concentration of the first type oftitanium oxide fine particle and the second type of titanium oxide fineparticle in the visible light-responsive photocatalytic titanium oxidefine particle dispersion is preferably from 0.01 to 20 wt %, andespecially from 0.5 to 10 wt %.

In addition, a binder may be added to the visible light-responsivephotocatalytic titanium oxide fine particle dispersion, both for thepurpose of making the dispersion easier to apply to the surfaces of thesubsequently described various types of members and also to make thefine particles readily adhering. Examples of binders include metalcompound-based binders that include silicon, aluminum, titanium,zirconium or the like, and organic resin-based binders that include afluoroplastic, an acrylic resin, a urethane resin or the like.

The binder is added and used in a weight ratio between the binder andthe titanium oxide, expressed as (binder/titanium oxide), of preferablyfrom 0.01 to 99, more preferably from 0.1 to 9, and even more preferablyfrom 0.4 to 2.5. The reason is that, at a weight ratio below 0.01,adherence of the titanium oxide fine particle to the surfaces of varioustypes of members may be inadequate, and at a weight ratio above 99, thevisible light activity may be inadequate.

In particular, to obtain an excellent photocatalytic thin film having ahigh photocatalysis and high transparency, it is especially desirablefor a silicon compound-based binder to be added and used in acompounding ratio (weight ratio between silicon compound and titaniumoxide) of preferably from 1:99 to 99:1, more preferably from 10:90 to90:10, and even more preferably from 30:70 to 70:30. Here, “siliconcompound-based binder” refers to a colloidal dispersion, solution oremulsion of a silicon compound that is obtained by including a solid orliquid silicon compound in an aqueous dispersion medium. Illustrativeexamples include colloidal silica (preferred particle size, 1 to 150nm); solutions of silicates; silane and siloxane hydrolyzate emulsions;silicone resin emulsions; and emulsions of copolymers of a siliconeresin with another resin, such as silicone-acrylic resin copolymers andsilicone-urethane resin copolymers.

<Method for Preparing Visible Light-Responsive Photocatalytic TitaniumOxide Fine Particle Dispersion>

The visible light-responsive photocatalytic titanium oxide fine particledispersion of the invention is produced by respectively preparing adispersion of the first type of titanium oxide fine particle (firsttitanium oxide fine particle dispersion) and a dispersion of the secondtype of titanium oxide fine particle (second titanium oxide fineparticle dispersion), and then mixing together the first titanium oxidefine particle dispersion and the second titanium oxide fine particledispersion.

The production method is exemplified by a method that includes thefollowing Steps (1) to (5):

-   (1) preparing a tin and transition metal constituent-containing    peroxotitanic acid solution from a starting titanium compound, a tin    compound, a transition metal compound (exclusive of an iron-group    element compound), a basic substance, hydrogen peroxide and an    aqueous dispersion medium;-   (2) preparing a tin and transition metal constituent-containing    titanium oxide fine particle dispersion by heating the tin and    transition metal constituent-containing peroxotitanic acid solution    prepared in Step (1) at between 80° C. and 250° C. and under    pressure control;-   (3) preparing an iron-group element and chromium-group element    constituent-containing peroxotitanic acid solution from a starting    titanium compound, an iron-group element compound, a chromium-group    element compound, a basic substance, hydrogen peroxide and an    aqueous dispersion medium;-   (4) preparing an iron-group element and chromium-group element    constituent-containing titanium oxide fine particle dispersion by    heating the iron-group element and chromium-group element    constituent-containing peroxotitanic acid solution prepared in    Step (3) at between 80° C. and 250° C. and under pressure control;    and-   (5) mixing together the two types of titanium oxide fine particle    dispersions prepared in Steps (2) and (4).

Steps (1) to (2) are steps for obtaining the first titanium oxide fineparticle dispersion, Steps (3) to (4) are steps for obtaining the secondtitanium oxide fine particle dispersion, and Step (5) is a final stepfor obtaining a dispersion containing both the first type of titaniumoxide fine particle and the second type of titanium oxide fine particle.

Because it is preferable, as already mentioned, to use at least onecompound from among molybdenum compounds, tungsten compounds andvanadium compounds as the transition metal compound employed in Step(1), the respective steps are described in detail below with this inmind.

Step (1):

In Step (1), a transition metal and tin constituent-containingperoxotitanic acid solution is prepared by reacting a starting titaniumcompound, a transition metal compound (exclusive of an iron-groupelement compound; the same applies below), a tin compound, a basicsubstance and a hydrogen peroxide in an aqueous dispersion medium.

The reaction method may be either a method that adds the basic substanceto the starting titanium compound in the aqueous dispersion medium toform titanium hydroxide, removes impurity ions other than the metallicions to be included, adds hydrogen peroxide to form peroxotitanic acid,and then adds the transition metal compound and the tin compound,thereby giving a transition metal and tin constituent-containingperoxotitanic acid; or a method that adds the transition metal compoundand the tin compound to the starting titanium compound and the basicsubstance in an aqueous dispersion medium and effects dissolution so asto form a transition metal and tin constituent-containing titaniumhydroxide, removes impurity ions other than the metallic ions to beincluded, and subsequently adds hydrogen peroxide, thereby giving atransition metal and tin constituent-containing peroxotitanic acid.

Moreover, in the first stage of the latter method, the starting titaniumcompound and the basic substance in the aqueous dispersion medium may beseparated into two aqueous dispersion media (two liquids), such as anaqueous dispersion medium in which the starting titanium compound isdispersed and an aqueous dispersion medium in which the basic substanceis dispersed, and the transition metal compound and the tin compound maybe dissolved in one or both of these two liquids, depending on thesolubilities of these respective compounds in the two liquids, afterwhich both solutions may be mixed together.

After a transition metal and tin constituent-containing peroxotitanicacid solution is thus obtained, the solution is furnished to thehydrothermal reaction in subsequently described Step (2), therebyenabling titanium oxide fine particles in which these respective metalsare present in solid solution in titanium oxide to be obtained.

Examples of the starting titanium compound include inorganic acid saltsof titanium, such as chlorides, nitrates, and sulfates; organic acidsalts such as the titanium salts of formic acid, citric acid, oxalicacid, lactic acid and glycolic acid; and the titanium hydroxide thatsettles out when hydrolysis is carried out by adding an alkali toaqueous solutions of these. Such starting titanium compounds may be usedsingly or two or more may be used in combination. Of these, the use oftitanium chlorides (TiCl₃, TiCl₄) is preferred.

The transition metal compound, the tin compound and the aqueousdispersion medium, each of which has been described above, are used insuch a way as to achieve the above-described formulation. Theconcentration of the aqueous solution of starting titanium compoundformed of the starting titanium compound and the aqueous dispersionmedium is preferably 60 wt % or less, and more preferably 30 wt % orless. The concentration lower limit is set as appropriate, although aconcentration of at least 1 wt % is generally preferred.

The purpose of the basic substance is to smoothly convert the startingtitanium compound into titanium hydroxide. Illustrative examples includehydroxides of alkali metals or alkaline earth metals, such as sodiumhydroxide and potassium hydroxide; and amine compounds such as ammonia,alkanolamines and alkylamines. The basic substance is added and used inan amount such as to bring the pH of the aqueous solution of thestarting titanium compound to 7 or above, and especially from 7 to 10.The basic substance may be used together with the aqueous dispersionmedium after first being rendered into an aqueous solution of a suitableconcentration.

The purpose of the hydrogen peroxide is to convert the starting titaniumcompound or titanium hydroxide into a peroxotitanium, that is, atitanium oxide compound containing a Ti—O—O—Ti bond, and is typicallyused in the form of hydrogen peroxide water. The amount of hydrogenperoxide added is preferably set to from 1.5 to 20 times moles per thetotal moles of transition metal, vanadium and tin combined. When addinghydrogen peroxide and converting the starting titanium compound ortitanium hydroxide into peroxotitanic acid, the reaction temperature ispreferably set to between 5° C. and 80° C. and the reaction time ispreferably set to from 30 minutes to 24 hours.

The resulting transition metal and tin constituent-containingperoxotitanic acid solution may, for the sake of pH adjustment, etc.,include an alkaline substance or an acidic substance. Illustrativeexamples of what is referred to here as the alkaline substance includeammonia, sodium hydroxide, calcium hydroxide and alkylamine.Illustrative examples of the acidic substance include inorganic acidssuch as sulfuric acid, nitric acid, hydrochloric acid, carbonic acid,phosphoric acid and hydrogen peroxide; and organic acids such as formicacid, citric acid, oxalic acid, lactic acid and glycolic acid. The pH ofthe transition metal and tin-containing peroxotitanic acid solutionobtained at this time is from 1 to 9, with a pH of from 4 to 7 beingpreferred from the standpoint of safety during handling.

Step (2):

In Step (2), the transition metal and tin constituent-containingperoxotitanic acid solution obtained in Step (1) is furnished to ahydrothermal reaction under pressure control and a temperature ofbetween 80° C. and 250° C., preferably between 100° C. and 250° C., for0.01 to 24 hours. From the standpoint of reaction efficiency andreaction controllability, a reaction temperature of between 80° C. and250° C. is suitable. As a result, the transition metal and tinconstituent-containing peroxotitanic acid is converted to transitionmetal and tin constituent-containing titanium oxide fine particles.Here, “under pressure control” means to carry out suitablepressurization in such a way as to be able to maintain the reactiontemperature in cases where the reaction temperature exceeds the boilingpoint of the dispersion medium. This includes control at atmosphericpressure in cases where the temperature is at or below the boiling pointof the dispersion medium. The pressure used here is generally from about0.12 MPa to about 4.5 MPa, preferably from about 0.15 MPa to about 4.5MPa, and more preferably from about 0.20 MPa to about 4.5 MPa. Thereaction time is preferably from 1 minute to 24 hours. Step (2) thusprovides a dispersion of the transition metal and tinconstituent-containing titanium oxide fine particle that serve as thefirst type of titanium oxide fine particle.

The particle size of the titanium oxide fine particle thus obtained ispreferably in the range already mentioned above, although control of theparticle size by adjusting the reaction condition is possible. Forexample, the particle size can be made smaller by shortening thereaction time and the temperature rise time.

Step (3):

In Step (3), separate from above Steps (1) to (2), an iron-group elementand chromium-group element constituent-containing peroxotitanic acidsolution is prepared by reacting a starting titanium compound, aniron-group element compound, a chromium-group element compound, a basicsubstance and hydrogen peroxide in an aqueous dispersion medium. Asidefrom using an iron-group element compound and a chromium-group elementcompound in place of the transition metal compound and the tin compoundin Step (1), the reaction is carried out in exactly the same way.

That is, as the starting materials, these being a starting titaniumcompound (the same as the starting titanium compound for the first typeof titanium oxide fine particle), an iron group compound, a chromiumgroup compound, an aqueous dispersion medium, a basic substance andhydrogen peroxide, each of which has been described above, are used insuch a way as to achieve the above-described formulation, and thenfurnished to a reaction under the temperature and time conditionsmentioned above.

The resulting iron-group element and chromium-group elementconstituent-containing peroxotitanic acid solution may include also analkaline substance or an acidic substance in order to, for example,adjust the pH. The alkaline substance and acidic substance, and pHadjustment as well, may be handled in the same way as described above.

Step (4):

In Step (4), the iron-group element and chromium-group elementconstituent-containing peroxotitanic acid solution obtained in Step (3)is furnished to a hydrothermal reaction under pressure control and atemperature of between 80° C. and 250° C., preferably between 100° C.and 250° C., for 0.01 to 24 hours. From the standpoint of reactionefficiency and reaction controllability, a reaction temperature ofbetween 80° C. and 250° C. is suitable. As a result, the iron-groupelement and chromium-group element constituent-containing peroxotitanicacid is converted to iron-group element and chromium-group elementconstituent-containing titanium oxide fine particle. Here, “underpressure control” means to carry out suitable pressurization in such away as to be able to maintain the reaction temperature in cases wherethe reaction temperature exceeds the boiling point of the dispersionmedium. This includes control at atmospheric pressure in cases where thetemperature is at or below the boiling point of the dispersion medium.The pressure used here is generally from about 0.12 MPa to about 4.5MPa, preferably from about 0.15 MPa to about 4.5 MPa, and morepreferably from 0.20 MPa to 4.5 MPa. The reaction time is preferablyfrom 1 minute to 24 hours. This Step (4) provides a dispersion of theiron-group element and chromium-group element constituent-containingtitanium oxide fine particle that serve as the second type of titaniumoxide fine particle.

The particle size of the titanium oxide fine particle thus obtained ispreferably in the range already mentioned above, although control of theparticle size by adjusting the reaction conditions is possible. Forexample, the particle size can be made smaller by shortening thereaction time and the temperature rise time.

Step (5):

In Step (5), the first titanium oxide fine particle dispersion obtainedfrom Steps (1) to (2) and the second titanium oxide fine particledispersion obtained from Steps (3) to (4) are mixed together. The mixingmethod is not particularly limited, and may consist of agitation with anagitator or dispersion with an ultrasonic disperser. The temperature atthe time of mixture is preferably between 20° C. and 100° C., and themixing time is preferably from 1 minute to 3 hours. As for the mixingratio, mixing should be carried out in such a way that the weight ratiobetween the titanium oxide fine particles in the respective titaniumoxide fine particle dispersions becomes the weight ratio alreadydescribed above.

The weights of the titanium oxide fine particles contained in therespective titanium oxide fine particle dispersions can be calculatedfrom the weights and concentrations of the respective titanium oxidefine particle dispersions. Using the following formula, theconcentration of the titanium oxide fine particle dispersion can becalculated from the weight of the nonvolatile matter (titanium oxidefine particle) remaining and the weight of the sampled titanium oxidefine particle dispersion after a portion of the titanium oxide fineparticle dispersion is sampled and heated at 105° C. for 3 hours toevaporate the solvent thereof.

Concentration (%) of titanium oxide fine particle dispersion=[weight ofnonvolatile matter (g)/weight of titanium oxide fine particle dispersion(g)]×100

As noted above, from the standpoint of the ease of forming aphotocatalytic thin film of the required thickness, the totalconcentration of the first type of titanium oxide fine particle and thesecond type of titanium oxide fine particle in the visiblelight-responsive photocatalytic titanium oxide fine particle dispersionthus produced is preferably from 0.01 to 20 wt %, and more preferablyfrom 0.5 to 10 wt %. With regard to adjustment of the concentration,when the concentration is higher than the desired concentration, theconcentration can be lowered by adding aqueous solvent to dilute thedispersion; when the concentration is lower than the desiredconcentration, the concentration can be increased by evaporating orfiltering off some of the aqueous solvent. The concentration can bedetermined as described above.

In case where the above-described film formability-increasing binder isadded, such addition is preferably carried out to a visiblelight-responsive photocatalytic titanium oxide fine particle dispersionwhose concentration has been adjusted as described above, such that thedesired concentration is achieved following mixture of the aqueousbinder solution to be added.

<Member Having Photocatalytic Thin Film on Surface>

The visible light-responsive photocatalytic titanium oxide fine particledispersion of the invention can be used to form a photocatalytic film onthe surface of various kinds of members. Here, the various kinds ofmembers are not particularly limited and the materials making up themembers are exemplified by organic materials and inorganic materials.These members can have a variety of shapes depending on their respectivepurposes and intended applications.

Illustrative examples of the organic materials include synthetic resinmaterials such as vinyl chloride resin (PVC), polyethylene (PE),polypropylene (PP), polycarbonate (PC), acrylic resin, polyacetal,fluoroplastic, silicone resin, ethylene-vinyl acetate copolymers (EVA),acrylonitrile-butadiene rubber (NBR), polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyvinyl butyral (PVB), ethylene-vinylalcohol copolymer (EVOH), polyimide resin, polyphenylene sulfide (PPS),polyetherimide (PEI), polyetheretherimide (PEED, polyetheretherketone(PEEK), melamine resin, phenolic resin andacrylonitrile-butadiene-styrene (ABS) resin; natural materials such asnatural rubber; and semi-synthetic materials made of the above syntheticresin materials and natural materials. These materials may be renderedinto products of a required shape and construction, such as films,sheets, textile materials, textile products and other moldings orlaminates.

Examples of the inorganic materials include nonmetallic inorganicmaterials and metallic inorganic materials. Examples of nonmetallicinorganic materials include glass, ceramic and stone. These may berendered into products of various forms, such as tile, glass, mirrors,walls and decorative materials. Examples of metallic inorganic materialsinclude cast iron, steel, iron, ferrous alloys, aluminum, aluminumalloys, nickel, nickel alloys and diecast zinc. These may be plated withthe above metallic inorganic materials or coated with the above organicmaterials, or may be platings applied to the surface of the aboveorganic materials or nonmetallic inorganic materials.

Of the various above members, the visible light-responsivephotocatalytic titanium oxide fine particle dispersion of the inventionis especially useful for producing transparent photocatalytic thin filmson PET and other polymer films.

The method of forming a photocatalytic thin film on the surface ofvarious kinds of members may be one in which the visiblelight-responsive photocatalytic titanium oxide fine particle dispersionis coated onto the surface of the member by a known coating method suchas spray coating or dip coating, and then dried by a known drying methodsuch as far-infrared drying, drying by induction heating or hot-airdrying. The thickness of the photocatalytic thin film may be variouslyselected, although a thickness in the range of from 10 nm to 10 μm isgenerally preferred.

A film of the above-described visible light-responsive photocatalytictitanium oxide fine particle mixture is thereby formed. In this case,when a binder is included in the above-indicated amount within the abovedispersion, a film is formed that contains both a titanium oxidefine-particle mixture and a binder.

The photocatalytic thin film formed in this way is transparent and notonly provides, as in the prior art, good photocatalysis when exposed tolight in the ultraviolet region (10 to 400 nm), but can also achieveexcellent photocatalysis even when exposed only to visible-spectrumlight (400 to 800 nm) from which conventional photocatalysts have beenunable to obtain sufficient photocatalysis. Owing to photocatalysis bythe titanium oxide, the various kinds of members on which thisphotocatalytic thin film has been formed decompose organic matteradsorbed to the surface, and can therefore exhibit such effects ascleaning, deodorizing and disinfection of the member surface.

EXAMPLES

The invention is illustrated more fully below by way of Working Examplesand Comparative Examples, although these Examples are not intended tolimit the invention. The various measurements in the invention werecarried out as described below.

(1) Average Particle Size (D₅₀) of Titanium Oxide Fine Particles inDispersion

The average particle size (D₅₀) of titanium oxide fine particles in adispersion was measured by using the particle size analyzer (trade name:“Nanotrac UPA-EX150”; from Nikkiso Co., Ltd.).

(2) Test of Photocatalytic Thin-Film Performance in Decomposition ofAcetaldehyde Gas (Under LED Irradiation)

The activity of a photocatalytic thin film produced by application anddrying of the dispersion was evaluated by means of acetaldehyde gasdecomposition reactions. Evaluation was carried out as follows by abatch-type method for evaluating gas decomposition performance.

An evaluation sample obtained by forming a photocatalytic thin filmcontaining about 20 mg (dry weight) of photocatalytic fine particles onthe entire surface of an A4-size (210 mm×297 mm) PET film was set withina 5-liter capacity stainless steel cell having a quartz glass window,following which the cell was filled with 5 ppm concentrationacetaldehyde gas that was moisture-conditioned to 50% humidity and thesample was exposed to light at an illuminance of 30,000 Lx from an LEDlamp (model number: TH-211×200SW, from CCS Inc.; spectral distribution,400 to 800 nm) positioned at the top of the cell. When acetaldehyde gasdecomposes on account of the photocatalyst on the thin film, theconcentration of acetaldehyde gas within the cell decreases. Bymeasuring the concentration, it is possible to determine the amount ofacetaldehyde gas that has decomposed. The acetaldehyde gas concentrationwas measured with a photoacoustic multigas monitor (trade name: INNOVA1412, from LumaSense Technologies Inc.), and the lengths of timerequired for the concentration of acetaldehyde gas to decrease from theinitial concentration of 5 ppm to [1] 1 ppm and to [2] 0.03 ppm wereevaluated based on the following criteria. The tests were performed forup to 50 hours.

[1] Time Required for Concentration to Decrease to 1 ppm

-   -   Good (◯): Decreased to 1 ppm within 10 hours    -   Marginal (Δ): Decreased to 1 ppm within 25 hours    -   No Good (x): Decrease to 1 ppm took 25 hours or more, or        concentration did not decrease to 1 ppm

[2] Time Required for Concentration to Decrease to 0.03 ppm

-   -   Good (◯): Decreased to 0.03 ppm within 20 hours    -   Marginal (Δ): Decreased to 0.03 ppm within 50 hours    -   No Good (x): Decrease to 0.03 ppm took 50 hours or more, or        concentration did not decrease to 0.03 ppm

(3) Identification of Crystal Phase of Titanium Oxide Fine Particle

The crystal phase of the titanium oxide fine particle was identified bypowder x-ray diffraction analysis (using a desktop x-ray powderdiffractometer available under the trade name D2 PHASER from Bruker AXS)on the titanium oxide fine particle powder recovered by drying theresulting titanium oxide fine particle dispersion at 105° C. for 3hours.

Working Example 1 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Tin and Molybdenum in Solid Solution>

A tin and molybdenum-containing titanium hydroxide precipitate wasobtained by adding and dissolving tin(IV) chloride in a 36 wt % aqueoussolution of titanium(IV) chloride to a Ti/Sn molar ratio of 20, dilutingthis ten-fold with pure water, and then gradually adding 10 wt % ammoniawater in which molybdenum(VI) oxide had been added and dissolved to aTi/Mo molar ratio of 20 based on the titanium constituent in the aqueoussolution of titanium(IV) chloride, thereby effecting neutralization andhydrolysis. The pH at this time was 8. The resulting precipitate wasdeionization-treated by repeated addition of pure water and decantation.Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated tin and molybdenum-containing titanium hydroxideprecipitate to a H₂O₂/(Ti+Sn+Mo) molar ratio of 10, after which thesystem was stirred at 50° C. for three hours to fully carry out thereaction, thereby giving a clear, orange-colored tin andmolybdenum-containing peroxotitanic acid solution (a).

A 500 mL autoclave was charged with 400 mL of the tin andmolybdenum-containing peroxotitanic acid solution (a), and this washydrothermally treated at 150° C. for 90 minutes. Next, theconcentration was adjusted by adding pure water, thereby giving adispersion (solids concentration, 1 wt %) of titanium oxide fineparticle (A) containing tin and molybdenum in solid solution. Powderx-ray diffraction analysis was carried out on the titanium oxide fineparticle (A), whereupon the only observed peaks were rutile-typetitanium oxide peaks, indicating that the tin and molybdenum were insolid solution in the titanium oxide.

<Preparation of Dispersion of Titanium Oxide Fine Particle ContainingIron and Tungsten in Solid Solution>

An iron and tungsten-containing titanium hydroxide precipitate wasobtained by adding and dissolving iron(III) chloride in a 36 wt %aqueous solution of titanium(IV) chloride to a Ti/Fe molar ratio of 10,diluting this ten-fold with pure water, and then gradually adding 10 wt% ammonia water in which sodium tungstate(VI) had been added anddissolved to a Ti/W molar ratio of 33 based on the titanium constituentin the aqueous solution of titanium(IV) chloride, thereby effectingneutralization and hydrolysis. The pH at this time was 8. The resultingprecipitate was deionization-treated by repeated addition of pure waterand decantation. Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated iron and tungsten-containing titanium hydroxideprecipitate to a H₂O₂/(Ti+Fe+W) molar ratio of 8, after which the systemwas stirred at 40° C. for two hours to fully carry out the reaction,thereby giving a clear, orange-colored iron and tungsten-containingperoxotitanic acid solution (b).

A 500 mL autoclave was charged with 400 mL of the iron andtungsten-containing peroxotitanic acid solution (b), and this washydrothermally treated at 130° C. for 90 minutes. Next, theconcentration was adjusted by adding pure water, thereby giving adispersion (solids concentration, 1 wt %) of titanium oxide fineparticle (B) containing iron and tungsten in solid solution. Powderx-ray diffraction analysis was carried out on the titanium oxide fineparticle (B), whereupon the only observed peaks were anatase-typetitanium oxide peaks, indicating that the iron and tungsten were insolid solution in the titanium oxide.

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-1) was obtained by mixing together the respectivedispersions of titanium oxide fine particle (A) and titanium oxide fineparticle (B) to a weight ratio of the titanium oxide fine particle (A)to the titanium oxide fine particle (B), expressed as (A):(B), of 50:50.

A coating liquid for evaluation was produced by adding a silica-basedbinder (colloidal silica available under the trade name Snotex 20 fromNissan Chemical Industries, Ltd.; average particle size, 10 to 20 nm; anaqueous solution having a SiO₂ concentration of 20 wt %) to thephotocatalytic titanium oxide fine particle dispersion (E-1) so as togive a TiO₂/SiO₂ weight ratio of 1.5.

The coating liquid for evaluation was coated onto an A4-size PET filmwith a #7 wire bar coater in such a way as to form a photocatalytic thinfilm (thickness, about 80 nm) containing 20 mg of photocatalytictitanium oxide fine particle and dried for one hour in an oven set to80° C., thereby giving a sample member for evaluation of theacetaldehyde gas decomposition performance. The acetaldehyde gasdecomposition performance of this photocatalytic thin film was measuredby using the batch-type gas decomposition performance evaluation method,whereupon, following LED irradiation (wavelength, 400 to 800 nm), theacetaldehyde gas concentration decreased to 1 ppm in 5.1 hours (◯) andto 0.03 ppm in 10.8 hours (◯).

Working Example 2 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Tin and Molybdenum in Solid Solution>

Aside from adding tin(IV) chloride to a Ti/Sn molar ratio of 33 andmolybdenum(VI) oxide to a Ti/Mo molar ratio of 3.3 and setting thehydrothermal treatment time to 120 minutes, a dispersion of titaniumoxide fine particle (C) containing tin and molybdenum in solid solution(solids concentration, 1 wt %) was obtained in the same way as inWorking Example 1. Powder x-ray diffraction analysis was carried out onthe titanium oxide fine particle (C), whereupon the only observed peakswere rutile-type titanium oxide peaks and anatase-type titanium oxidepeaks, indicating that the tin and molybdenum were in solid solution inthe titanium oxide.

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-2) according to the invention was obtained by mixingtogether the respective dispersions of titanium oxide fine particle (C)and titanium oxide fine particle (B) to a weight ratio of the titaniumoxide fine particle (C) to the titanium oxide fine particle (B),expressed as (C):(B), of 50:50.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-2) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in7.3 hours (O) and to 0.03 ppm in 15.4 hours (O).

Working Example 3 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Tin and Tungsten in Solid Solution>

A tin and tungsten-containing titanium hydroxide precipitate wasobtained by adding and dissolving tin(IV) chloride in a 36 wt % aqueoussolution of titanium(IV) chloride to a Ti/Sn molar ratio of 5, dilutingthis ten-fold with pure water, and then gradually adding 10 wt % ammoniawater in which sodium tungstate(VI) had been added and dissolved to aTi/W molar ratio of 10 based on the titanium constituent in the aqueoussolution of titanium(IV) chloride, thereby effecting neutralization andhydrolysis. The pH at this time was 8. The resulting precipitate wasdeionization-treated by repeated addition of pure water and decantation.Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated tin and tungsten-containing titanium hydroxideprecipitate to a H₂O₂/(Ti+Sn+W) molar ratio of 10, after which thesystem was stirred at 50° C. for three hours to fully carry out thereaction, thereby giving a clear, orange-colored tin andtungsten-containing peroxotitanic acid solution (d).

A 500 mL autoclave was charged with 400 mL of the tin andtungsten-containing peroxotitanic acid solution (d), and this washydrothermally treated at 180° C. for 90 minutes. Next, theconcentration was adjusted by adding pure water, thereby giving adispersion (solids concentration, 1 wt %) of titanium oxide fineparticle (D) containing tin and tungsten in solid solution. Powder x-raydiffraction analysis was carried out on the titanium oxide fine particle(D), whereupon the only observed peaks were rutile-type titanium oxidepeaks, indicating that the tin and tungsten were in solid solution inthe titanium oxide.

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-3) was obtained by mixing together the respectivedispersions of titanium oxide fine particle (D) and titanium oxide fineparticle (B) to a weight ratio of the titanium oxide fine particle (D)to the titanium oxide fine particle (B), expressed as (D):(B), of 50:50.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-3) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in6.2 hours (O) and to 0.03 ppm in 13.1 hours (O).

Working Example 4 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Tin, Molybdenum and Tungsten in Solid Solution>

A tin, molybdenum and tungsten-containing titanium hydroxide precipitatewas obtained by adding and dissolving tin(IV) chloride in a 36 wt %aqueous solution of titanium(IV) chloride to a Ti/Sn molar ratio of 20,diluting this ten-fold with pure water, and then gradually adding 10 wt% ammonia water in which molybdenum(VI) oxide had been added anddissolved to a Ti/Mo molar ratio of 50 and sodium tungstate(VI) had beenadded and dissolved to a Ti/W molar ratio of 20 based on the titaniumconstituent in the aqueous solution of titanium(IV) chloride, therebyeffecting neutralization and hydrolysis. The pH at this time was 8. Theresulting precipitate was deionization-treated by repeated addition ofpure water and decantation. Next, 35 wt % hydrogen peroxide water wasadded to the deionization-treated tin, molybdenum andtungsten-containing titanium hydroxide precipitate to aH₂O₂/(Ti+Sn+Mo+W) molar ratio of 10, after which the system was stirredat 80° C. for three hours to fully carry out the reaction, therebygiving a clear, orange-colored tin, molybdenum and tungsten-containingperoxotitanic acid solution (e).

A 500 mL autoclave was charged with 400 mL of the tin, molybdenum andtungsten-containing peroxotitanic acid solution (e), and this washydrothermally treated at 150° C. for 90 minutes. Next, theconcentration was adjusted by adding pure water, thereby giving adispersion (solids concentration, 1 wt %) of titanium oxide fineparticle (E) containing tin, molybdenum and tungsten in solid solution.Powder x-ray diffraction analysis was carried out on the titanium oxidefine particle (E), whereupon the only observed peaks were rutile-typetitanium oxide peaks, indicating that the tin, molybdenum and tungstenwere in solid solution in the titanium oxide.

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-4) was obtained by mixing together the respectivedispersions of titanium oxide fine particle (E) and titanium oxide fineparticles (B) to a weight ratio of the titanium oxide fine particle (E)to the titanium oxide fine particles (B), expressed as (E):(B), of70:30.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-4) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in3.9 hours (O) and to 0.03 ppm in 8.0 hours (O).

Working Example 5 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Tin and Vanadium in Solid Solution>

A tin and vanadium-containing titanium hydroxide precipitate wasobtained by adding and dissolving tin(IV) chloride in a 36 wt % aqueoussolution of titanium(IV) chloride to a Ti/Sn molar ratio of 20 andvanadyl(IV) sulfate to a Ti/V molar ratio of 2,000, diluting thisten-fold with pure water, and then gradually adding 10 wt % ammoniawater, thereby effecting neutralization and hydrolysis. The pH of thesolution at this time was 8.5. The resulting precipitate wasdeionization-treated by repeated addition of pure water and decantation.Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated tin and vanadium-containing titanium hydroxideprecipitate to a H₂O₂/(Ti+Sn+V) molar ratio of 10, after which thesystem was stirred at 50° C. for three hours to fully carry out thereaction, thereby giving a clear, orange-colored tin andvanadium-containing peroxotitanic acid solution (f).

A 500 mL autoclave was charged with 400 mL of the tin andvanadium-containing peroxotitanic acid solution (f), and this washydrothermally treated at 150° C. for 90 minutes. Next, theconcentration was adjusted by adding pure water, thereby giving adispersion (solids concentration, 1 wt %) of titanium oxide fineparticle (F) containing tin and vanadium in solid solution. Powder x-raydiffraction analysis was carried out on the titanium oxide fine particle(F), whereupon the only observed peaks were rutile-type titanium oxidepeaks, indicating that the tin and vanadium were in solid solution inthe titanium oxide.

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-5) was obtained by mixing together the respectivedispersions of titanium oxide fine particle (F) and titanium oxide fineparticle (B) to a weight ratio of the titanium oxide fine particle (F)to the titanium oxide fine particle (B), expressed as (F):(B), of 90:10.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-5) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in9.5 hours (O) and to 0.03 ppm in 19.2 hours (O).

Working Example 6 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Iron and Molybdenum in Solid Solution>

An iron and molybdenum-containing titanium hydroxide precipitate wasobtained by adding and dissolving iron(III) chloride in a 36 wt %aqueous solution of titanium(IV) chloride to a Ti/Fe molar ratio of 10,diluting this ten-fold with pure water, and then gradually adding 10 wt% ammonia water in which molybdenum(VI) oxide was added and dissolved toa Ti/Mo molar ratio of 5 based on the titanium constituent in theaqueous solution of titanium(IV) chloride, thereby effectingneutralization and hydrolysis. The pH at this time was 8. The resultingprecipitate was deionization-treated by repeated addition of pure waterand decantation. Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated iron and molybdenum-containing titanium hydroxideprecipitate to a H₂O₂/(Ti+Fe+Mo) molar ratio of 8, after which thesystem was stirred at 50° C. for two hours to fully carry out thereaction, thereby giving a clear, orange-colored iron andmolybdenum-containing peroxotitanic acid solution (g).

A 500 mL autoclave was charged with 400 mL of the iron andmolybdenum-containing peroxotitanic acid solution (g), and this washydrothermally treated at 130° C. for 120 minutes. Next, theconcentration was adjusted by adding pure water, thereby giving adispersion (solids concentration, 1 wt %) of titanium oxide fineparticle (G) containing iron and molybdenum in solid solution. Powderx-ray diffraction analysis was carried out on the titanium oxide fineparticle (G), whereupon the only observed peaks were anatase-typetitanium oxide peaks, indicating that the iron and molybdenum were insolid solution in the titanium oxide.

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-6) was obtained by mixing together the respectivedispersions of titanium oxide fine particle (A) and titanium oxide fineparticle (G) to a weight ratio of the titanium oxide fine particle (A)to the titanium oxide fine particle (G), expressed as (A):(G), of 50:50.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-6) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in6.5 hours (O) and to 0.03 ppm in 14.6 hours (O).

Working Example 7 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Iron and Tungsten in Solid Solution>

Aside from adding iron(III) chloride to a Ti—Fe molar ratio of 6.6,adding sodium tungstate(VI) to a Ti/W molar ratio of 10 and setting thehydrothermal treatment temperature to 120° C. and the hydrothermaltreatment time to 180 minutes, a dispersion (solids concentration, 1 wt%) of titanium oxide fine particle (H) containing iron and tungsten insolid solution was obtained in the same way as in Working Example 1.Powder x-ray diffraction analysis was carried out on the titanium oxidefine particle (H), whereupon the only observed peaks were anatase-typetitanium oxide peaks, indicating that the iron and tungsten were insolid solution in the titanium oxide.

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-7) was obtained by mixing together the respectivedispersions of titanium oxide fine particle (E) and titanium oxide fineparticle (H) to a weight ratio of the titanium oxide fine particle (E)to the titanium oxide fine particle (H), expressed as (E):(H), of 70:30.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-7) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in3.2 hours (O) and to 0.03 ppm in 6.8 hours (O).

Working Example 8

A visible light-responsive photocatalytic titanium oxide fine particledispersion (E-8) according to the invention was obtained by mixingtogether respective dispersions of titanium oxide fine particle (A),titanium oxide fine particle (D) and titanium oxide fine particle (H) tothe weight ratio (A):(D):(H)=35:35:30.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-8) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in4.4 hours (O) and to 0.03 ppm in 8.5 hours (O).

Working Example 9

A visible light-responsive photocatalytic titanium oxide fine-particledispersion (E-9) according to the invention was obtained by mixingrespective dispersions of titanium oxide fine particle (A), titaniumoxide fine particle (B) and titanium oxide fine particle (G) to theweight ratio (A):(B):(G)=40:30:30.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the photocatalytic titanium oxide fine particle dispersion(E-9) in the same way as in Working Example 1. The acetaldehyde gasdecomposition performance was measured, whereupon, following LEDirradiation, the acetaldehyde gas concentration decreased to 1 ppm in9.3 hours (O) and to 0.03 ppm in 19.3 hours (O).

Comparative Example 1

A titanium oxide fine particle dispersion (C-1) was obtained using onlya dispersion of titanium oxide fine particles (A).

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-1) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased only to 4.5 ppm even when 50hours had elapsed (x).

Comparative Example 2

A titanium oxide fine-particle dispersion (C-2) was obtained using onlya dispersion of titanium oxide fine particles (B).

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-2) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, adecrease in the acetaldehyde gas concentration was not observed evenwhen 50 hours had elapsed (x).

Comparative Example 3 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Iron in Solid Solution>

An iron-containing titanium hydroxide precipitate was obtained by addingand dissolving iron(III) chloride in a 36 wt % aqueous solution oftitanium(IV) chloride to a Ti/Fe molar ratio of 10, diluting thisten-fold with pure water, and then gradually adding 10 wt % ammoniawater to the resulting aqueous solution, thereby effectingneutralization and hydrolysis. The pH at this time was 8. The resultingprecipitate was deionization-treated by repeated addition of pure waterand decantation. Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated iron-containing titanium hydroxide precipitate to aH₂O₂/(Ti+Fe) molar ratio of 8, after which the system was stirred at 40°C. for two hours to fully carry out the reaction, thereby giving aclear, orange-colored iron-containing peroxotitanic acid solution (i).

A 500 mL autoclave was charged with 400 mL of the iron-containingperoxotitanic acid solution (i), and this was hydrothermally treated at130° C. for 90 minutes. Next, the concentration was adjusted by addingpure water, thereby giving a dispersion (solids concentration, 1 wt %)of titanium oxide fine particle (I) containing iron in solid solution.Powder x-ray diffraction analysis was carried out on the titanium oxidefine particle (I), whereupon the only observed peaks were anatase-typetitanium oxide peaks, indicating that the iron was in solid solution inthe titanium oxide.

A titanium oxide fine particle dispersion (C-3) was obtained using onlythe dispersion of titanium oxide fine particle (I).

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-3) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, adecrease in the acetaldehyde gas concentration was not observed evenwhen 50 hours had elapsed (x).

Comparative Example 4 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Copper in Solid Solution>

A copper-containing titanium hydroxide precipitate was obtained byadding and dissolving copper(II) chloride in a 36 wt % aqueous solutionof titanium(IV) chloride to a Ti/Cu molar ratio of 20, diluting thisten-fold with pure water, and then gradually adding 10 wt % ammoniawater, thereby effecting neutralization and hydrolysis. The pH at thistime was 7.5. The resulting precipitate was deionization-treated byrepeated addition of pure water and decantation. Next, 35 wt % hydrogenperoxide water was added to the deionization-treated copper-containingtitanium hydroxide precipitate to a H₂O₂/(Ti+Cu) molar ratio of 12,after which the system was stirred at 40° C. for three hours to fullycarry out the reaction, thereby giving a clear, green-coloredcopper-containing peroxotitanic acid solution (j).

A 500 mL autoclave was charged with 400 mL of the copper-containingperoxotitanic acid solution (j), and this was hydrothermally treated at130° C. for 90 minutes. Next, the concentration was adjusted by addingpure water, thereby giving a dispersion (solids concentration, 1 wt %)of titanium oxide fine particle (J) containing copper in solid solution.Powder x-ray diffraction analysis was carried out on the titanium oxidefine particle (J), whereupon the only observed peaks were anatase-typetitanium oxide peaks, indicating that the copper was in solid solutionin the titanium oxide.

A titanium oxide fine particle dispersion (C-4) was obtained using onlythe dispersion of titanium oxide fine particle (J).

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-4) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased only to 4.6 ppm in 50 hours(x).

Comparative Example 5

A titanium oxide fine-particle dispersion (C-5) was obtained by mixingtogether a dispersion of titanium oxide fine particle (A) and adispersion of titanium oxide fine particle (I) to the weight ratio(A):(I)=50:50.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-5) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased to 1 ppm in 12.5 hours (Δ) andto 0.03 ppm in 30.5 hours (Δ).

Comparative Example 6

A titanium oxide fine particle dispersion (C-6) was obtained by mixingtogether respective dispersions of titanium oxide fine particle (A) andtitanium oxide fine particle (J) to the weight ratio (A):(J)=70:30.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-6) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased to 1 ppm in 17.1 hours (◯) andto 0.2 ppm in 50 hours (x).

Comparative Example 7

A titanium oxide fine particle dispersion (C-7) was obtained by mixingtogether respective dispersions of titanium oxide fine particle (D) andtitanium oxide fine particle (I) to the weight ratio (D):(I)=50:50.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-7) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased to 1 ppm in 15.0 hours (Δ) andto 0.03 ppm in 48.2 hours (Δ).

Comparative Example 8 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Tin in Solid Solution>

A tin-containing titanium hydroxide precipitate was obtained by addingand dissolving tin(IV) chloride in a 36 wt % aqueous solution oftitanium(IV) chloride to a Ti/Sn molar ratio of 20, diluting thisten-fold with pure water, and then gradually adding 10 wt % ammoniawater, thereby effecting neutralization and hydrolysis. The pH at thistime was 9. The resulting precipitate was deionization-treated byrepeated addition of pure water and decantation. Next, 35 wt % hydrogenperoxide water was added to the deionization-treated tin-containingtitanium hydroxide precipitate to a H₂O₂/(Ti+Sn) molar ratio of 6, afterwhich the system was stirred at room temperature for one full day andnight to fully carry out the reaction, thereby giving a clear,orange-colored tin-containing peroxotitanic acid solution (k).

A 500 mL autoclave was charged with 400 mL of the tin-containingperoxotitanic acid solution (k), and this was hydrothermally treated at150° C. for 90 minutes. Next, the concentration was adjusted by addingpure water, thereby giving a dispersion (solids concentration, 1 wt %)of titanium oxide fine particle (K) containing tin in solid solution.Powder x-ray diffraction analysis was carried out on the titanium oxidefine particle (K), whereupon the only observed peaks were rutile-typetitanium oxide peaks, indicating that the tin was in solid solution inthe titanium oxide.

A titanium oxide fine-particle dispersion (C-8) was obtained by mixingtogether respective dispersions of titanium oxide fine particle (K) andtitanium oxide fine particle (B) to the weight ratio (K):(B)=70:30.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-8) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased to 1 ppm in 39.6 hours (x) andto 0.9 ppm in 50 hours (x).

Comparative Example 9 <Preparation of Dispersion of Titanium Oxide FineParticle Containing Molybdenum in Solid Solution>

A molybdenum-containing titanium hydroxide precipitate was obtained bydiluting a 36 wt % aqueous solution of titanium(IV) chloride ten-foldwith pure water, adding to this aqueous solution and dissolvingmolybdenum(VI) oxide to a Ti/Mo molar ratio of 20 with respect to thetitanium constituent in the aqueous solution of titanium(IV) chloride,and then gradually adding 10 wt % ammonia water, thereby effectingneutralization and hydrolysis. The pH at this time was 8. The resultingprecipitate was deionization-treated by repeated addition of pure waterand decantation. Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated molybdenum-containing titanium hydroxideprecipitate to a H₂O₂/(Ti+Mo) molar ratio of 8, after which the systemwas stirred at room temperature for one full day and night to fullycarry out the reaction, thereby giving a clear, orange-coloredmolybdenum-containing peroxotitanic acid solution (1).

A 500 mL autoclave was charged with 400 mL of the molybdenum-containingperoxotitanic acid solution (1), and this was hydrothermally treated at130° C. for 120 minutes. Next, the concentration was adjusted by addingpure water, thereby giving a dispersion (solids concentration, 1 wt %)of titanium oxide fine particle (L) containing molybdenum in solidsolution. Powder x-ray diffraction analysis was carried out on thetitanium oxide fine particle (L), whereupon the only observed peaks wereanatase-type titanium oxide peaks, indicating that the molybdenum was insolid solution in the titanium oxide.

A titanium oxide fine-particle dispersion (C-9) was obtained by mixingtogether respective dispersions of titanium oxide fine particle (L) andtitanium oxide fine particle (B) to the weight ratio (L):(B)=50:50.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-9) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased only to 4.7 ppm even when 50hours had elapsed (x).

Comparative Example 10 <Preparation of Titanium Oxide Fine-ParticleDispersion>

A titanium hydroxide precipitate was obtained by diluting a 36 wt %aqueous solution of titanium(IV) chloride ten-fold with pure water andthen gradually adding 10 wt % ammonia water, thereby effectingneutralization and hydrolysis. The pH at this time was 9. The resultingprecipitate was deionization treated by repeated addition of pure waterand decantation. Next, 35 wt % hydrogen peroxide water was added to thedeionization-treated titanium hydroxide precipitate to a H₂O₂/Ti molarratio of 5, after which the system was stirred at room temperature forone full day and night to fully carry out the reaction, thereby giving aclear, yellow-colored peroxotitanic acid solution (m).

A 500 mL autoclave was charged with 400 mL of the peroxotitanic acidsolution (m), and this was hydrothermally treated at 130° C. for 90minutes. Next, the concentration was adjusted by adding pure water,thereby giving a dispersion (solids concentration, 1 wt %) of titaniumoxide fine particle (M). Powder x-ray diffraction analysis was carriedout on the titanium oxide fine particle (M), whereupon the observedpeaks were anatase-type titanium oxide peaks.

A titanium oxide fine-particle dispersion (C-10) was obtained by usingonly the dispersion of titanium oxide fine particle (M).

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-10) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration did not decrease even when 50 hours hadelapsed (x).

Comparative Example 11

<Recovery of Dissolved Constituent from Dispersion of Titanium OxideFine Particle Containing Iron in Solid Solution>

The dispersion of titanium oxide fine particle (I) containing iron insolid solution was centrifugally separated at 210,000×g with a smallultracentrifuge (available under the trade name Himac CS150NX fromHitachi Koki Co., Ltd.) into titanium oxide fine particle (I) containingiron in solid solution, solvent and dissolved constituent. Theconcentration of dissolved iron constituent in the solvent, as measuredwith an inductively coupled plasma (ICP) emission spectrometer(available under the trade name ICP Emission Spectrometer IRIS 1000 fromThermo Fisher Scientific), was 2.2 ppm, indicating that substantiallyall of the iron constituent added had entered into solid solution in thetitanium oxide fine particle is and become insoluble constituent.

A titanium oxide fine particle dispersion (C-11) was obtained by mixingtogether the dispersion of titanium oxide fine particle (A) with thesolvent and dissolved constituent obtained by separating off thetitanium oxide fine particle (I) from the dispersion of titanium oxidefine particle (I) with an ultracentrifuge, to a weight ratio between thetitanium oxide fine particle (A) and the solvent and dissolvedconstituent, expressed as (A):(I dissolved constituent), of 50:50.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-11) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased only to 4.8 ppm even when 50hours had elapsed (x).

Comparative Example 12 <Preparation of Dispersion of Titanium Oxide FineParticle Having Iron Constituent Adsorbed to (Supported on) Surface>

A dispersion (C-12) of titanium oxide fine particle having an ironconstituent adsorbed to the surface was obtained by mixing together adispersion of titanium oxide fine particle (A) and an aqueous solutionof iron(III) chloride dissolved in pure water to a concentration of 1 wt%, to a weight ratio between the titanium oxide fine particle (A) andthe iron of 100:0.05.

A coating liquid for evaluation and a photocatalytic thin film wereproduced from the titanium oxide fine particle dispersion (C-12) in thesame way as in Working Example 1. The acetaldehyde gas decompositionperformance was measured, whereupon, following LED irradiation, theacetaldehyde gas concentration decreased to 1 ppm in 23.0 hours (Δ), andthe acetaldehyde gas concentration decreased to 0.8 ppm in 50 hours (x).

Comparative Example 13 <Preparation of Dispersion of Titanium Oxide FineParticle Having Iron Constituent Adsorbed to (Supported on) Surface>

A dispersion of titanium oxide fine particle (A) and an aqueous solutionof iron(III) chloride obtained by dissolving iron(III) chloride in purewater to a concentration of 1 wt % were mixed together to a weight ratioof the titanium oxide fine particle (A) to the iron of 100:0.5,whereupon titanium oxide fine particle in the dispersion (C-13)agglomerated and precipitated out, and so the evaluation was stopped. Amethod in which an iron group compound is added in this way to adispersion worsens the dispersed state of the titanium oxide fineparticle within the dispersion, greatly limiting the amount that can beadded. In addition, the stability of the liquid also worsens.

Table 1 collectively presents the starting material ratios, hydrothermaltreatment conditions and average particle sizes (D₅₀) for the titaniumoxide fine particles used in Working Examples 1 to 9 and ComparativeExamples 1 to 13.

TABLE 1 Hydrothermal Titanium oxide treatment Average fine particleMolar ratios of starting materials Temp. Time particle dispersion Ti/SnTi/Mo Ti/W Ti/V Ti/Fe Ti/Cu (° C.) (min) size nm (A) 20 20 150 90 12 (B)33 10 130 90 13 (C) 33 3.3 150 120  12 (D) 5 10 180 90  7 (E) 20 50 20150 90  9 (F) 20 2,000 150 90  9 (G) 5 10 130 120  18 (H) 10 6.6 120180  12 (I) 10 130 90 18 (J) 20 130 90 18 (K) 20 150 90 10 (L) 20 130120  16 (M) 130 90 20

Table 2 collectively presents the mixing ratios, average particles sizesand acetaldehyde gas decomposition test results for the visiblelight-responsive photocatalytic fine particle dispersions obtained inWorking Examples 1 to 9 and Comparative Examples 1 to 13.

TABLE 2 Evaluation results Average Titanium oxide dispersion particle80% 99.4% Evaluation Mixing size reduction reduction sample Type rationm 1 ppm (hr) Rating 0.03 ppm (hr) Rating Working 1 E-1 (A) (B) 50:50 135.1 ◯ 10.8 ◯ Example 2 E-2 (C) (B) 50:50 12 7.3 ◯ 15.4 ◯ 3 E-3 (D) (B)50:50 10 6.2 ◯ 13.1 ◯ 4 E-4 (E) (B) 70:30 11 3.9 ◯  8.0 ◯ 5 E-5 (F) (B)90:10 10 9.5 ◯ 19.2 ◯ 6 E-6 (A) (G) 50:50 15 6.5 ◯ 14.6 ◯ 7 E-7 (E) (H)70:30 11 3.2 ◯  6.8 ◯ 8 E-8 (A), (D) (H) 35:35:30 10 4.4 ◯  8.5 ◯ 9 E-9(A) (B), (G) 40:30:30 14 9.3 ◯ 19.3 ◯ Comparative 1 C-1 (A) 100:0 12 50hrs, 4.5 ppm x 50 hrs, 4.5 ppm x Example 2 C-2 (B) 0:100 13 no decreasex no decrease x 3 C-3 (I) 0:100 18 no decrease x no decrease x 4 C-4 (J)0:100 18 50 hr, 4.6 ppm x 50 hr, 4.6 ppm x 5 C-5 (A) (I) 50:50 15 12.5 Δ 30.5  Δ 6 C-6 (A) (J) 70:30 16 17.1  Δ 50 hr, 0.2 ppm x 7 C-7 (D) (I)50:50 14 15.0  Δ 48.2  Δ 8 C-8 (K) (B) 70:30 11 39.6  x 50 hr, 0.9 ppm x9 C-9 (L) (B) 50:50 15 50 hr, 4.7 ppm x 50 hr, 4.7 ppm x 10  C-10 (M)0:100 20 no decrease x no decrease x 11  C-11 (A) (I) 50:50 12 50 hr,4.8 ppm x 50 hr, 4.8 ppm x dissolved constituents 12  C-12 (A) iron 0.05to 100 23 23.0  Δ 50 hr, 0.8 ppm x chloride TiO₂ solution (aq) 13  C-13(A) iron 0.5 to 100 — Evaluation was stopped chloride TiO₂ becausedipersion incurred solution agglomeration and precipitation (aq)

As is apparent from the results in Working Examples 1 to 9, by mixingtogether a first type of titanium oxide fine particle containing insolid solution a tin constituent and a transition metal constituent thatincreases visible light responsiveness (molybdenum constituent, tungstenconstituent, vanadium constituent) and a second type of titanium oxidefine particle containing in solid solution an iron group constituent anda chromium group constituent, even with a small amount of photocatalyst,the acetaldehyde gas decomposition is good even under irradiation withan LED lamp that emits only light in the visible region. Moreover, theacetaldehyde gas concentration can be lowered within an effective timeperiod such as 50 hours or less, and preferably 20 hours or less, to thelevel of 0.03 ppm or below which is the indoor concentration guidelinevalue for a chemical substance (acetaldehyde) within indoor airestablished by the Japanese Ministry of Health, Labor and Welfare.

As is apparent from the results in Comparative Examples 1 and 2, asufficient photocatalytic activity under visible light irradiationcannot be obtained with the first type of titanium oxide fine particlealone or the second type of titanium oxide fine particle alone.

As is apparent from the results in Comparative Examples, 2, 3, 4 and 10,in cases where, respectively, titanium oxide fine particle containingiron in solid solution, titanium oxide fine particle containing iron anda chromium group constituent (tungsten) in solid solution, titaniumoxide fine particle containing copper in solid solution and titaniumoxide fine particle that do not contain any dissimilar metals in solidsolution are used alone, no activity whatsoever is obtained undervisible light irradiation. This behavior differs from when titaniumoxide particle containing copper in solid solution is used alone.

As is apparent from the results in Comparative Examples 5 and 7, wheniron alone is selected as the metal contained in solid solution in thesecond type of titanium oxide fine particle, the time required foracetaldehyde gas decomposition is longer and the photocatalytic activityis lower than when both iron and a chromium group constituent areselected as the metals contained in solid solution within the secondtype of titanium oxide fine particle shown in the respective WorkingExamples.

As is apparent from the results in Comparative Example 6, when copper isselected as the metal contained in solid solution in the second type oftitanium oxide fine particle, under visible light irradiation,decomposition occurs initially when the acetaldehyde concentration ishigh, but a sufficient photocatalytic activity on low-concentrationacetaldehyde gas is not obtained. By contrast, as shown in each of theWorking Examples, when an iron group constituent and a chromium groupconstituent are selected as the metals contained in solid solution inthe second type of titanium oxide fine particle, it is obtained not onlya rapid decomposition rate when the acetaldehyde gas concentration ishigh, but also a photocatalytic activity even when the acetaldehyde gasconcentration is low, making it possible to lower the concentration to0.03 ppm or below.

As is apparent from the results in Comparative Examples 8 and 9, whenthe metal contained in solid solution in the first type of titaniumoxide fine particle is tin alone or a transition metal alone, asufficient photocatalytic activity cannot be obtained under visiblelight irradiation. Therefore, in order to obtain a high activity undervisible light irradiation, it is necessary to add tin and a transitionmetal constituent that increases the visible light responsiveness to thefirst type of titanium oxide fine particle.

As is apparent from the results in Comparative Example 11, the secondtype of titanium oxide fine particle is essential for increasing thevisible light activity, and an iron constituent which is dissolved inthe dispersion rather than being contained in solid solution in thesecond type of titanium oxide fine particle does not contribute toincreased activity. That is, the chief factor in the visible lightactivity-increasing effect is not an iron constituent that leaks fromthe second type of titanium oxide fine particle; rather, it depends onthe combination of the second type of titanium oxide fine particlecontaining in solid solution an iron group constituent and a chromiumgroup constituent with the first type of titanium oxide fine particlecontaining in solid solution tin and a transition metal constituentwhich increases the visible light responsiveness.

Moreover, as is apparent form the results of Comparative Examples 12 and13, although a dissolved iron constituent does contribute somewhat toincreased visible light activity, a sufficient visible light activity onlow-concentration acetaldehyde gas is not obtained. Also, when adissolved iron constituent is added in a large amount, this may causethe titanium oxide fine particles within the dispersion to agglomerateand precipitate out.

INDUSTRIAL APPLICABILITY

The visible light-responsive photocatalytic fine particle dispersions ofthe invention are useful for the production of photocatalytic thin filmsby coating onto various types of substrates made of inorganic materialssuch as glass or metal or made of organic materials such as polymerfilms (e.g., PET films), and are particularly useful for producingtransparent photocatalytic thin films on polymer films.

1. A visible light-responsive photocatalytic titanium oxide fineparticle mixture comprising two types of titanium oxide fine particles:a first type of titanium oxide fine particle containing in solidsolution a tin constituent and a transition metal constituent (exclusiveof an iron-group element constituent) that increases visible lightresponsiveness, and a second type of titanium oxide fine particlecontaining in solid solution an iron-group element constituent and achromium-group element constituent.
 2. The visible light-responsivephotocatalytic titanium oxide fine particle mixture of claim 1, whereinthe first type of titanium oxide fine particle and the second type oftitanium oxide fine particle have a mixing ratio therebetween, expressedas the weight ratio [(first type of titanium oxide fineparticle)/(second type of titanium oxide fine particle)], of from 99 to0.01.
 3. The visible light-responsive photocatalytic titanium oxide fineparticle mixture of claim 1 or 2, wherein the amount of the tinconstituent included in the first type of titanium oxide fine particle,expressed as a molar ratio with titanium (Ti/Sn), is from 1 to 1,000. 4.The visible light-responsive photocatalytic titanium oxide fine particlemixture of claim 1, wherein the transition metal constituent containedin solid solution in the first type of titanium oxide fine particle isat least one selected from the group consisting of vanadium, chromium,manganese, niobium, molybdenum, rhodium, antimony, tungsten and cerium.5. The visible light-responsive photocatalytic titanium oxide fineparticle mixture of claim 4, wherein the transition metal constituentcontained in solid solution in the first type of titanium oxide fineparticle is at least one selected from the group consisting ofmolybdenum, tungsten and vanadium.
 6. The visible light-responsivephotocatalytic titanium oxide fine particle mixture of claim 5, whereinthe amount of the molybdenum or tungsten constituent included in thefirst type of titanium oxide fine particle, expressed as a molar ratiowith titanium (Ti/Mo or Ti/W), is from 1 to 1,000.
 7. The visiblelight-responsive photocatalytic titanium oxide fine particle mixture ofclaim 5, wherein the amount of the vanadium constituent included in thefirst type of titanium oxide fine particle, expressed as a molar ratiowith titanium (Ti/V), is from 10 to 10,000.
 8. The visiblelight-responsive photocatalytic titanium oxide fine particle mixture ofclaim 1, wherein the amount of the iron-group element constituentincluded in the second type of titanium oxide fine particle, expressedas a molar ratio with titanium (Ti/iron group element), is from 1 to1,000.
 9. The visible light-responsive photocatalytic titanium oxidefine particle mixture of claim 1, wherein the iron-group elementconstituent contained in solid solution in the second type of titaniumoxide fine particle is an iron constituent.
 10. The visiblelight-responsive photocatalytic titanium oxide fine particle mixture ofclaim 1, wherein the amount of the chromium-group element constituentincluded in the second type of titanium oxide fine particle, expressedas a molar ratio with titanium (Ti/chromium-group element), is from 1 to1,000.
 11. The visible light-responsive photocatalytic titanium oxidefine particle mixture of claim 1, wherein the chromium-group elementconstituent contained in solid solution in the second type of titaniumoxide fine particle is at least one selected from the group consistingof a molybdenum constituent and a tungsten constituent.
 12. A visiblelight-responsive photocatalytic titanium oxide fine particle dispersioncomprising two types of titanium oxide fine particles dispersed in anaqueous dispersion medium: a first type of titanium oxide fine particlecontaining in solid solution a tin constituent and a transition metalconstituent (exclusive of an iron-group element constituent) thatincreases visible light responsiveness, and a second type of titaniumoxide fine particle containing in solid solution an iron-group elementconstituent and a chromium-group element constituent.
 13. The visiblelight-responsive photocatalytic titanium oxide fine particle dispersionof claim 12, further comprising a binder.
 14. The visiblelight-responsive photocatalytic titanium oxide fine particle dispersionof claim 13, wherein the binder is a silicon compound-based binder. 15.A photocatalytic thin film comprising the visible light-responsivephotocatalytic titanium oxide fine particle mixture of claim
 1. 16. Thephotocatalytic thin film of claim 15, further comprising a binder.
 17. Amember in which the photocatalytic thin film of claim 15 or 16 is formedon the substrate surface.
 18. A method for preparing a visiblelight-responsive photocatalytic titanium oxide fine particle dispersion,comprising the steps of: (1) preparing a tin and transition metalconstituent-containing peroxotitanic acid solution from a startingtitanium compound, a tin compound, a transition metal compound(exclusive of an iron-group element compound), a basic substance, ahydrogen peroxide and an aqueous dispersion medium; (2) preparing a tinand transition metal constituent-containing titanium oxide fine particledispersion by heating at between 80° C. and 250° C. and under pressurecontrol the tin and transition metal constituent-containingperoxotitanic acid solution obtained in Step (1); (3) preparing aniron-group element and chromium-group element constituent-containingperoxotitanic acid solution from a starting titanium compound, aniron-group element compound, a chromium-group element compound, a basicsubstance, hydrogen peroxide and an aqueous dispersion medium; (4)preparing an iron-group element and chromium-group elementconstituent-containing titanium oxide fine particle dispersion byheating at between 80° C. and 250° C. and under pressure control theiron-group element and chromium-group element constituent-containingperoxotitanic acid solution obtained in Step (3); and (5) mixingtogether the two types of titanium oxide fine particle dispersionsprepared in Steps (2) and (4).